Problems of conditioning Xenopus laevis tadpoles with standard avoidance-response learning paradigms.

The amphibian Xenopus laevis embryo (tadpole) provides a satisfactory alternative to mammalian screening for structural teratogens. Testing was undertaken to extend the usefulness of this species for behavioral teratogenicity testing. One simple and eight operant conditioning paradigms were examined: none elicited learning in Xenopus embryos. Adaptation to the conditioning stimulus (light) and freezing in response to the unconditioned stimulus (shock) were responses incompatible with conditioned learning.